On Thu, Aug 16, 2012 at 04:38:14PM +0400, Cyrill Gorcunov wrote:
> On Thu, Aug 16, 2012 at 10:24:48AM +0400, Cyrill Gorcunov wrote:
> > > > > On the other hand, if you want a real filehandle then wouldn't you
> > > > > want
> > > > > to e.g. call the filesystem's ->encode_fh() if necessary, as
> > > > > exportfs_encode_fh() does?
> > > >
> > > > Well, one of the problem I hit when I've been trying to use encode_fh
> > > > is that every new implementation of encode_fh will require some size
> > > > (even unknown) in buffer where encoded data pushed. Correct me please
> > > > if I'm wrong. But with export_encode_inode_fh there is a small buffer
> > > > with pretty known size needed on stack needed for printing data in
> > > > fdinfo.
> > >
> > > You can just give encode_fh a too-small data and let it fail if it's not
> > > big enough.
> > >
> > > (In practice I think everyone supports NFSv3 filehandles which have a
> > > maximum size of 64 bytes.)
> >
> > I'll think about it, thanks!
>
> Hi Bruce, thinking a bit more I guess using general encode_fh is not that
> convenient since it operates with dentries while our fdinfo output deals
> with inodes. Thus I should either provide some new encode_fh variant
> which would deal with inodes directly without "parents".
I can't see why that wouldn't work.
> Which doesn't
> look for me anyhow better than the new export_encode_inode_fh helper.
That isn't going to work for filesystems that define their own
encode_fh:
$ git grep '\.encode_fh'
fs/btrfs/export.c: .encode_fh = btrfs_encode_fh,
fs/ceph/export.c: .encode_fh = ceph_encode_fh,
fs/fat/inode.c: .encode_fh = fat_encode_fh,
fs/fuse/inode.c: .encode_fh = fuse_encode_fh,
fs/gfs2/export.c: .encode_fh = gfs2_encode_fh,
fs/isofs/export.c: .encode_fh = isofs_export_encode_fh,
fs/nilfs2/namei.c: .encode_fh = nilfs_encode_fh,
fs/ocfs2/export.c: .encode_fh = ocfs2_encode_fh,
fs/reiserfs/super.c: .encode_fh = reiserfs_encode_fh,
fs/udf/namei.c: .encode_fh = udf_encode_fh,
fs/xfs/xfs_export.c: .encode_fh = xfs_fs_encode_fh,
mm/shmem.c: .encode_fh = shmem_encode_fh,
--b.
> After all, if the use of encode_fh become a mandatory rule we can easily
> extend fsnotify fdinfo output to support new scheme without breaking
> user space, because output looks like
>
> | fhandle-type: 1 f_handle: 49b1060023552153
>
> (ie if something is changed than these fields will be simply updated).
>
> Or maybe I miss something?
>
> Cyrill
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